Electrochemical device

ABSTRACT

An electrochromic device is provided comprising: at least one electrochromic element comprising (i) at least one material that is electrically conducting in at least one oxidation state and (ii) at least one electrochromic material, wherein said materials (i) and (ii) can be the same or different; at least one layer of a solidified electrolyte which is in direct electrical contact with said electrochromic element; and at least two electrodes comprising PEDOT-PSS, arranged side by side in a common plane and adapted for application of a voltage therebetween, one of said electrodes being in direct electrical contact with a component selected from said electrochromic element(s) and the other electrode(s) being in direct electrical contact with a component selected from said electrolyte layer(s) and said electrochromic element(s). Furthermore an electrochemically active element is provided comprising: a first layer comprising PEDOT-PSS mixed with an adhesion promoter, and a second layer comprising PANI, the second layer being deposited on top of and in direct electrical contact with 25 the fist layer.

FIELD OF THE INVENTION

The present invention is related to electrochemical devices, and inparticular to printable, electrochemically active elements andelectrochemical pixel devices based on conducting organic materials andelectrochromic materials. The invention also relates to a process forthe production of an electrochemical pixel device.

BACKGROUND OF THE INVENTION

Semiconducting and conducting organic materials, both polymers andmolecules, have successfully been included in a large range ofelectronic devices, e g electrochemical devices, for instance as dynamiccolorants in smart windows and in polymer batteries. Reversible dopingand de-doping involving mobile ions switches the material betweendifferent redox states.

Electrochromic materials exhibit colour changes or changes in opticaldensity as a result of electrochemical reduction and/or oxidationreactions. An electrochromic material can either be present as a solid,or exist as molecular, neutral or ionic species in an electrolytesolution. These materials have been used for the creation ofelectrochromic cells, where the passage of electric charge causes colourchanges in the materials. Electrochromic cells are used inelectrochromic devices of different kinds, and two principal categoriesof these devices can be distinguished. The two categories differ fromeach other mainly in the arrangement of the elements of theelectrochromic cell.

The first category of electrochromic devices utilises a sandwichconstruction, and is used in applications such as automobile windows,building windows, sunglasses, large billboards, mirrors with variablereflectance, sunroofs etc. In this type of electrochromic device,continuous layers of electrochromic material and electrolyte (as well asother layers of e g ion reservoir material) are confined between twoelectrodes that completely cover the layers of electrochromic materialand electrolyte. For the electrochromic device to be of use, at leastone of said electrodes has to be transparent to let light through thedevice. This requirement is met in the prior art through the use ofelectrode materials such as indium-doped tin oxide (ITO), tin dioxide orfluorine-doped tin dioxide. The electrochromic materials used in theseapplications vary, but are often based on heavy metal oxides such as WO₃or conducting polymers such as polyaniline or polypyrrole. Theconducting, electrochromic polymer poly-(3,4-ethylendioxythiophene)(PEDOT) has attracted much study, and sandwich devices incorporatingthis polymer have been realised.

The second category of electrochromic devices aim at providing anelectrically updateable display for realisation on a flexible support.U.S. Pat. No. 5,754,329 describes such a display, in which theelectrodes of the electrochromic device are placed in one and the sameplane, contacting a layer of electrochromic material for the generationof local colour effects at the interface between the electrochromicmaterial and the electrodes. U.S. Pat. No. 5,877,888 represents afurther development of this device, describing a two-sided display.However, the arrangement of the component layers of the electrochromicdevice is similar to that of the device of the U.S. Pat. No. 5,754,329,considering that the electrodes on either side of the display supportcontact electrochromic material only, and the generation ofelectrochromic effects is confined to the area of the electrodes. Theelectrochromic materials that are used in these devices are described indetail in U.S. Pat. No. 5,812,300.

Problems with the pixel matrices in the displays of the prior artmentioned above include the fact that they are difficult and expensiveto manufacture. In particular, no electrochemical pixel devices havebeen disclosed which are truly capable of being mass produced.Furthermore, the practical use of the pixel elements in the prior artdevices has been hampered by their comparatively high power consumptionas well as their short lifetimes. Also, materials used in prior artdevices suffer from a lack of environmental friendliness, processabilityand economic production possibilities. There is therefore a need for newand improved pixel devices for incorporation in matrices that may beused in displays.

Actually, the lifetime problem is found to be widespread and similarproblems are experienced in other types of electrochemical devices, suchas electrochemical diodes and transistors. One critical factor for thelifetime of such devices is the performance of their electrochemicallyactive elements, i.e. the element which is supposed to provide for redoxreactions. There is therefore a general need for improvedelectrochemically active elements, not only for pixel devices but alsofor any other type of electrochemical device.

SUMMARY OF THE INVENTION

One of the objects of the present invention is then to meet the abovesaid needs, by developing the art of electrochromic devices andelectrochemically active elements, and by providing a device withhandling, production, disposal and other characteristics superior tothose of the prior art.

Another object of the present invention is to provide an electrochromicdevice which can be deposited on a large range of different rigid orflexible substrates by conventional printing methods.

Yet another object of the present invention is to provide anenvironmentally safe electrochromic device, so that the disposal of thedevice, along with any support onto which it has been deposited, doesn'tgive rise to handling problems, and so that no safety restrictions haveto be imposed on the use of the device.

Still another object of the present invention is to make possible newapplications of conducting organic materials, using several differentproperties of such materials in combination.

A further object is to provide an electrochemically active element whichexhibits improved long-term stability and thus provides for increasedlifetimes of the elements.

A further object of the invention is to provide processes for theproduction of such devices, which processes utilise conventionalprinting methods or other deposition techniques that are well known,relatively unexpensive and easily scaled up.

The aforementioned objects are met by the invention as defined in theindependent claims. Specific embodiments of the invention are defined inthe dependent claims. In addition, the present invention has otheradvantages and features apparent from the detailed description below.

Thus, according to one aspect of the invention an electrochromic deviceis provided comprising: at least one electrochromic element comprising(i) at least one material that is electrically conducting in at leastone oxidation state and (ii) at least one electrochromic material,wherein said materials (i) and (ii) can be the same or different;

-   -   at least one layer of a solidified electrolyte which is in        direct electrical contact with said electrochromic element; and    -   at least two electrodes comprising PEDOT-PSS, arranged side by        side in a common plane and adapted for application of a voltage        therebetween, one of said electrodes being in direct electrical        contact with a component selected from said electrochromic        element(s) and the other electrode(s) being in direct electrical        contact with a component selected from said electrolyte layer(s)        and said electrochromic element(s).

The electrochromic element may be formed from the same material as theelectrodes, or from a different material. The electrodes are arrangedside by side in a plane and thus form an electrode layer, which can bedeposited on a support in a conventional manner and patterned in anydesirable fashion. Compared to ordinary, stacked or sandwichedelectrocromic elements, this lateral pixel configuration has manyadvantages. For example, the need for a transparent electrode iseliminated, since the electrochromic surface can be viewed directlythrough the electrolyte.

Furthermore, the PEDOT-PSS polymer (poly-(3,4-ethylendioxythiophene)doped with poly(styrene sulfonate)) combines electrical andelectrochromic properties; when reduced PEDOT-PSS is blue in colour ithas low electrical conductivity, and when oxidised PEDOT-PSS turnstransparent, its electrical conductivity is substantially increased.However, even when reduced, the electrical conductivity of PEDOT-PSS isgenerally enough to facilitate the electron transport needed for thepolymer to function as an electrode and thus to promote additionalelectrochemical reactions. This enables the PEDOT-PSS to function as anelectrode even in its low conducting state. Due to the combination ofelectrical conductivity and electrochromic properties, PEDOT-PSS can beused both as electrodes and as electrochemical elements in the inventiveelectrochromical devices. Thereby the manufacturing of the device issubstantially simplified, since only two active materials need to beused; PEDOT-PSS and a suitably chosen electrolyte. For example, it ispossible to use a prefabricated PEDOT-PSS laminate, which comprises aflexible substrate on which a continuous layer of PEDOT-PSS isdeposited.

Such prefabricated laminates are currently commercially available fromAgfa under the trade names Orgacon™ EL-350 and Orgacon™ EL-1500. Thedifference between these laminates is their electrical conductivity,orgacon™ EL-350 having a higher conductivity (lower surface resistance)than Orgacon™ EL-1500. For most pixel applications, Orgacon™ EL-350 isthe preferred choice. As it appears, the Orgacon™ EL-1500 has toomoderate a contrast ratio to be used in most displays applications.

The electrode pattern, as well as the electrochromic element, can thenbe patterned in the PEDOT-PSS layer using any known principle, as isfurther described below. Having patterned the polymer, a layer ofelectrolyte can be deposited onto the polymer, for example using aprinting technique.

However, a disadvantage using PEDOT-PSS as the electrocromic element isthat driving voltages in the range of 1.0-2.0 V are required for theelectrochromic reactions to occur. Such high voltages, especially incombination with an electrolyte that has a low ionic conductivity,results not only in the intended reduction of the cathode electrode,which provides a deep-blue colour, but also in a high degree ofoxidation of the anode electrode. This high degree of oxidation resultsin a so-called “overoxidation” of the PEDOT-PSS anode, which is assumedto correspond to an irreversible interruption of the conjugatedpi-system on the polythiophene backbone of the PEDOT-PSS polymer. As aconsequence, PEDOT-PSS permanently loses its electrical conductivity aswell as its electrochromic behaviour and thus cannot be switched back toits reduced state.

Furthermore, in case higher switching speeds are needed, drivingvoltages as high as 10 volts may be required, depending on the lateralsize of the pixel. Of course, using such high driving voltages forPEDOT-PSS elements dramatically increases the problems related tooveroxidation and short lifetimes.

The use of PEDOT-PSS for the electrochromic element thus involves alifetime problem in that it easily can be overoxidized, resulting in apermanent and substantial decrease in electrical conductivity.Overoxidation is partially a function of electric field density andoccurs if the polymer is exposed to a too high oxidative current.Therefore, due to their asymmetrical design overoxidation isparticularly problematic in lateral structures. In lateral structures,as opposed to vertical structures, the current has to flow laterally inthe electrolyte and such architectures are thus much more sensitive todifferences in electrical conductivity between the electrolyte and theelectrode or electrochromic element. In case the electrolyte has ahigher electrical conductivity than the electrochromic element, thecurrent will tend to flow in the electrolyte instead of theelectrochromic element or the counter electrode and the electric fieldat the electrolyte interfaces will thus be the strongest at the outerends of the electrolyte layer. In case the electrolyte has a lowerelectrical conductivity than the electrochromic element (which often isthe case for solidified electrolytes), the electric field will insteadbe the strongest at the opposite end of the electrochromic element, i.e.in the area closest to the counter electrode

One way of compensating for the effect of overoxidation (i.e. thereduced electrical conductivity) is to increase the driving voltage.However, increased driving voltages obviously increase the degradationof the electrochromic material and thus accelerate the overoxidationprocess even more.

Furthermore, for some applications lateral PEDOT-PSS pixels mightexhibit poor contrast between their different colour states, and theupdating time for such pixels might be too slow. The updating time canbe improved by increasing the driving voltage, for example to 5-10 V.However, such high driving voltages will rapidly render the PEDOT-PSSpolymer overoxidised.

To this end, the inventors have realised that the electrochromic elementadvantageously can be made out polyaniline, commonly called PANI. Thus,according to one embodiment of the invention, the electrochromic elementcomprises polyaniline.

The voltage needed in order to perform redox reactions in PANI issubstantially lower than that needed for PEDOT-PSS. Typically 1-2 V isneeded in order to oxidise or reduce PEDOT-PSS elements, whereas avoltage as low as 0.5 V might be sufficient for PANI elements.Furthermore, PANI deposited on top of PEDOT-PSS does not becomeoveroxidised as easily as PEDOT-PSS itself and the PEDOT-PSS layerunderneath the PANI layer is substantially protected from overoxidationas compared to uncoated PEDOT-PSS. Therefore, the above discussedlifetime problem is substantially reduced when using electrochemicalelements based on PANI. The combination of lower driving voltages andhigher threshold for overoxidation substantially reduces the lifetimeproblems related to overoxidation. In fact, using PANI in theelectrochromic element it is even possible to increase the drivingvoltage to 10 V, thus facilitating substantially faster switching of thepixel, without the electrochromic element being overoxidised. However,as stated above PEDOT-PSS is almost transparent (actually it is slightlyyellowish) when oxidised and turns blue when reduced. This is opposed toPANI, which is blue when oxidised and virtually transparent whenreduced. Therefore, using PANI instead of PEDOT-PSS in theelectrochromic element will invert the colour of the pixel. Whenoxidised it will turn blue and when reduced it will turn transparent. Ofcourse, this opposite colouring effect does not generally cause aproblem but affects the design of the pixel and the way in which it isdriven.

The electrochromic element can be placed in any structural relation toits corresponding electrode. For example, it can be applied as a layeronto the electrode, or it can be placed laterally in relation to theelectrode. However, placing the PANI element laterally in relation tothe electrode is problematic for some applications, due to the lowconductivity of PANI. If an electrochromic element based on PANI isplaced as a layer on top of the electrode, due care is needed whenreducing the electrochromic element so as to avid reducing also thePEDOT-PSS electrode. Otherwise the blue colour of reduced PEDOT-PSS willbe visible trough the reduced and thus transparent PANI and the pixelwill in fact switch from blue to blue, a property which obviously isunwanted for most applications.

An inventive pixel can thus be manufactured as follows: A first and asecond PEDOT-PSS electrode are printed on a substrate using anyconventional printing method. Alternatively, a layer of Baytron P™,commercially available from Bayer AG, can be drop cast on to thesubstrate. Thereafter, a layer of PANI is printed on top of the firstelectrode, thus forming the electrochromically active element.Alternatively, the layer of PANI is printed next to and in contact withthe first electrode. Finally, a layer of electrolyte is applied over atleast parts of the electrochromic element and the second electrode.Actually, only the parts covered by electrolyte will function aselectrochemically active elements.

However, PEDOT-PSS exhibits hydrophilic properties when in contact withPANI diluted in organic solvent. Therefore, applying PANI directly ontoPEDOT-PSS might involve some problems. This is the case for example whentrying to spin coat an Orgacon™ EL-350 foil with PANI. The hydrophiliccharacter of the PEDOT-PSS surface is due to the enrichment of PSS onthe surface, since PSS is very hydrophilic. This problem is for examplenoticed for the above described prefabricated PEDOT-PSS laminates likeOrgacon™ El-350. The problem of adhereing PANI on to PEDOT-PSS is notlimited to the mere application process. The resulting PEDOT-PSS/PANIlaminate might also delaminate at a later stage, when the element is inuse. For example, when switching the element between different redoxstates, PANI and PEDOT-PSS layers might exhibit different swelling orexpansion properties, thus causing stress in the joint between the twomaterials.

To this end, the inventors have realised that these problems can beeliminated in a novel and unexpected way. As it turns out, adhesion issubstantially improved when using PEDOT-PSS in the form of screenprinting pastes, e.g. Orgacon™ EL as provided by Agfa. Such screenprinting inks have been “diluted” with different binders/“bulk fillers”,such as polystyrene, which in effect function as adhesion promoters whenPANI is subsequently applied. Furthermore, such screen printing pastesexhibit a substantially moderated electrochromic effect. Thus, accordingto one embodiment the electrodes are formed out of a mixture comprisingPEDOT-PSS and an adhesion promoter. It has been found that a mixturesuch as Orgacon™ EL, which mainly consists of PEDOT-PSS and polystyrene,organises itself in a web-like configuration when printed on asubstrate. An interconnected web of PEDOT-PSS is formed, which embracesa large number of small polystyrene “islands” or dots. As it appears,the web of PEDOT-PSS provides for electrical conductivity, while thepolystyrene dots, which typically occupy a larger fraction of thesurface, counteract the hydrophilic properties of the mixture. Thus, amixture of PEDOT-PSS and polystyrene is found to provide a materialwhich has sufficient electrical conductivity, which is not hydrophilicin relation to PANI, and which thus is an excellent material to use forthe electrodes. Furthermore, the apparent electrochromic effect isreduced as compared to pure PEDOT-PSS and consequently the mixture doesnot interfere with optical effects displayed by the PANI-basedelectrochromic element.

Using PEDOT-PSS/polystyrene electrodes, PANI electrochromic elements areeasily printed or casted directly on a portion of one of the electrodes,thus providing for even better contact between the electrode and theelement.

An electrochromic pixel can thus be manufactured as follows. First, theelectrodes are printed on a substrate using a mixture of PEDOT-PSS andan adhesion promoter (for example Orgacon™ EL) by means of anyconventional printing technique. Second, at least one of the electrodesis covered by a layer of PANI. Finally, the electrochromic element iscovered by a layer of transparent electrolyte.

The inventors have further more realised that the adhesion of PANI ontoa PEDOT-PSS/polystyrene mixture can be further improved by using PANIthat is cast from a toluene solution (such as PANIPOL™ T™, commerciallyavailable from PANIPOL). Thus, according to one embodiment of theinvention, the polyaniline in the electrochromic element is cast from atoluene solution.

As a basis for the invention, several circumstances are realized andutilized in a synergetic manner, namely:

-   -   The voltage needed in order to provide electrochromical effects        in PANI is substantially lower than the voltage needed in order        to provide electrochromical effects in PEDOT-PSS.    -   Through mixing of PEDOT-PSS with an adhesion promoter such as        polystyrene, the hydrophilic effect exhibited by pure PEDOT-PSS        in relation to PANI can be eliminated. Thus, a mixture of        PEDOT-PSS and polystyrene is easily coated with a layer of PANI.    -   A mixture of PEDOT-PSS and a suitably chosen adhesion promoter,        such as polystyrene, exhibits reduced electrochromic properties        as compared to pure PEDOT-PSS. Thus, a printed such mixture does        not change colour or conductivity to the same extent as does        PEDOT-PSS PSS such as Orgacon™ EL-350 or films cast from Baytron        P™.    -   The adhesion of PANI onto a mixture of PEDOT-PSS and an adhesion        promoter, such as Orgacon™ EL, is substantially enhanced when        using PANI that is cast from a toluene solution.    -   A higher voltage, facilitating faster switching, is tolerated by        the combination of PANI and PEDOT-PSS elements as compared to        PEDOT-PSS element only.    -   An electrolyte having lower electrical conductivity may be used        when the electrochemic/electrochromic element is based on PANI        as compared to the PEDOT-PSS case, since the electrolyte        controls a large portion of the electric field distribution in        the device.    -   The contrast ratio is substantially improved using        electrochromic elements based on PANI instead of PEDOT-PSS.        As a basis for the invention, it is thus recognized that these        circumstances can be exploited in an synergetic manner in order        to provide improved electrochromic and electrochemical elements.

In embodiments of the invention, an electrochromic device is provided,which comprises at least one further electrochromic material tocomplement said electrochromic material in the electrochromic element.This makes it possible to realise devices with more than one colour,with for example one colour-generating oxidation reaction and onecolour-generating reduction reaction taking place simultaneously atdifferent locations in the device. For example, an electrochromic devicehaving two electrochromic elements, one based on PEDOT-PSS and one basedon PEDOT-PSS/PANI, provides similar colouring effects in both elements.When the PEDOT-PSS/PANI element is reduced, the PEDOT-PSS element isoxidised and both consequently turn transparent. On the other hand, whenthe PEDOT-PSS/PANI element is oxidised, the PEDOT-PSS element is reducedand both turn blue. Using this combination, it is possible to maximisethe pixel area of the device, since both electrodes can form part of thevisible area of the display. As a further example, redox reactionsgiving rise to different colours at the same location, but at differentapplied voltages, can be designed. This further electrochromic materialcan be provided within the solidified electrolyte or within theelectrochromic element, which then for example comprises anelectrochromic redox pair.

Embodiments of the electrochromic device of the invention may alsocomprise a redox active material which does not in itself give rise toelectrochromic effects. Such a material may fulfil any or both of thefollowing two roles: (i) In some arrangements of the electrochromicdevice, the electrochromic material of the entire volume of theelectrochromic element can not be completely oxidised or reduced in theabsence of a complementary redox reaction; rather, only part of thematerial will be oxidised or reduced, respectively. Thus, the additionof a further redox active material makes it possible to fully oxidise orreduce the electrochromic material. (ii) The electrocromic material maybe sensitive to overoxidation, occurring at too high an applied voltage,and destroying the electrochromic material rendering it useless. Afurther redox active material comprised in the device may serve thefunction of protecting the electrocromic material from suchoveroxidation, through restricting the electric polarisation in theelectrochromic element to a value below a threshold value. At thisthreshold value, the protective, further redox active material willinstead be oxidised, protecting the electrochromic material from apolarisation that would otherwise destroy it. As is readily appreciatedby the skilled man in the light of what is discussed above, a suitablychosen redox active material, exhibiting electrochromic effects, couldserve the function of providing a complementary, colour-generatingreaction, at the same time as it provides either or both of thebeneficial effects of protection against overoxidation and enabling ofcomplete reduction/oxidation of the first electrochromic material. Ineffect, this is the case for the above discussed device having oneelectrochromic element based on PEDOT-PSS and one based onPEDOT-PSS/PANI.

In some embodiments of the electrochromic device of the invention,dynamic or variable colouring effects in the electrochromic device maybe generated through use of a combination of different solidifiedelectrolytes, having different ionic conductivities. Parts of anelectrochromic element, or some of a plurality of electrochromicelements, may then be in direct electrical contact with such differentelectrolytes. Electrochromic areas that are in contact with anelectrolyte having higher ionic conductivity will colour/decolour fasterthan electrochromic areas that are in contact with an electrolyte havinga lesser ionic conductivity, which makes possible different combinationsof image elements with different colouring and decolouring speeds.

For the successful operation of the electrochromic device, it comprisesa solidified electrolyte. The electrolyte enables the electrochemicalreactions resulting in a colour change in the electrochromic element.The solidified electrolyte is as defined in the “Materials” sectionbelow. The electrochromic device according to the invention isadvantageous in that it can be easily realised on a support, such aspolymer film or paper. Thus, the different components can be depositedon the support by means of conventional printing techniques such asscreen printing, offset printing, ink-jet printing and flexographicprinting, or coating techniques such as knife coating, doctor bladecoating, extrusion coating and curtain coating, such as described in“Modern Coating and Drying Technology” (1992), eds E D Cohen and E BGutoff, VCH Publishers Inc, New York, N.Y., USA. The polymers utilisedin the invention can also be deposited through in situ polymerisation bymethods such as electropolymerisation, UV-polymerisation, thermalpolymerisation and chemical polymerisation. As an alternative to theseadditive techniques for patterning of the components, it is alsopossible to use subtractive techniques, such as local destruction ofmaterial through chemical or gas etching, by mechanical means such asscratching, scoring, scraping or milling, or by any other subtractivemethods known in the art. Alternatively, overoxidative patterning ofPEDOT-PSS as described in the co-pending patent applicationPCT/SE02/01663 can be. exploited.

According to a preferred embodiment of the invention, the electrochromicdevice is encapsulated, in part or entirely, for protection of thedevice. The encapsulation retains any solvent needed for e g thesolidified electrolyte to function, and also keeps oxygen fromdisturbing the electrochemical reactions in the device. Encapsulationcan be achieved through liquid phase processes. Thus, a liquid phasepolymer or organic monomer can be deposited on the device using methodssuch as spray-coating, dip-coating or any of the conventional printingtechniques listed above. After deposition, the encapsulant can behardened for example by ultraviolet or infrared irradiation, by solventevaporation, by cooling or through the use of a two-component system,such as an epoxy glue, where the components are mixed together directlyprior to deposition. Alternatively, the encapsulation is achievedthrough lamination of a solid film onto the electrochemical pixeldevice. In preferred embodiments of the invention, in which thecomponents of the electrochemical pixel device are arranged on asupport, this support can function as the bottom encapsulant. In thiscase encapsulation is made more convenient in that only the top of thesheet needs to be covered with liquid phase encapsulant or laminatedwith solid film.

The inventors have furthermore realised that a mixture of PEDOT-PSS andpolystyrene coated with a layer of PANI provides an excellent activeelecrochemical element also for other applications than aselectrochromic elements. For example, such an element can be used aselectrodes in electrochemical transistors, diodes or pixels. In suchapplications, the PANI layer serves to protect the PEDOT-PSS electrodefrom overoxidation. The fact that the element happens to change colouris for these applications only to be seen as a side effect. As comparedto pure PEDOT-PSS, this novel element exhibits a substantially increasedresistance from being overoxidised. The electrical conductivity isvirtually the same as for pure PEDOT-PSS, and thus substantially betterthan for pure PANI.

Thus, according to another aspect of the invention, an electrochemicallyactive element is provide comprising:

a first layer comprising PEDOT-PSS mixed with an adhesion promoter; and

-   -   a second layer comprising PANI, the second layer being deposited        on top of and in direct electrical contact with the first layer.

This novel electrochemical element thus provides for excellentelectrical conductivity and excellent switching properties, i.e. thedifference in electrical conductivity between its redox states issubstantial. It furthermore provides for enhanced protection againstoveroxidation, as compared to pure PEDOT-PSS. On the other hand, ascompared to pure PANI the inventive element provides substantiallyimproved electrical conductivity. In essence, the inventive elementcombines the individual advantages of PEDOT-PSS and PANI into one singleelement.

According to one embodiment, said adhesion promoter comprisespolystyrene.

According to one embodiment, the layer of PANI is cast from a toluenesolution. As mentioned previously, such PANI provides for enhancedadhesiveness to the PEDOT-PSS/polystyrene mixture.

According to one embodiment, the electrochemically active element formspart of a pixel device.

The application of PANI onto PEDOT-PSS provides a number of additionaladvantages. First, since PANI is not as easily overoxidised as isPEDOT-PSS, the PANI layer provides a protective buffer. When oxidising aprotected piece of PEDOT-PSS, the redox reaction will be localised tothe layer of PANI without it being overoxidised. If the redox reactionis limited in time, the redox reaction might not even affect thePEDOT-PSS at all. Second, when the layer of PANI is oxidised, itselectrical conductivity will be reduced. Since the speed of theoxidation process is a function of the applied voltage, the oxidationwill be asymmetrically distributed in cases where the current densitydistribution is asymmetrical. In areas where the current density is thehighest, the layer of PANI will be most strongly oxidised and thus its Gconductivity reduced and, in effect, the current density redistributedso as to provide additional protection for particularly exposed portionsof the PEDOT-PSS. This method can advantageously be used in themanufacture of various polymer based electrochemical devices, such astransistors, diodes, and pixel elements.

Further objects and purposes of the present invention will be clear fromthe following drawings and detailed description of specific embodimentsthereof. These specifications and drawings are intended as illustrationsof the invention as claimed, and are not to be seen as limiting in anyway.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a top view of elements of one embodiment of anelectrochemical pixel device according to the invention interconnectedwith a transistor device.

FIG. 2 shows a top view of a similar device as shown in FIG. 1 buthaving the transistor part omitted.

FIGS. 3, 4 and 5 show various embodiments of the inventiveelectrochemically active element.

FIG. 6 shows a cross section of an electrochemically active element.

FIG. 7 shows a top view of an electrochromic device according to theinvention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Definitions:

Redox state: when reference is made to changes in the “redox state” ofthe electrochromic element, this is intended to include cases where thematerial in the element is either oxidised or reduced, as well as caseswhere there is a redistribution of charges within the element, so thatone end is reduced and the other end is oxidised. In the latter case,the element as a whole retains its overall redox state, but its redoxstate has nevertheless been changed according to the definition usedherein, due to the internal redistribution of charge carriers.

Electrochromic element: an “electrochromic element” in the devices ofthe invention is a continuous geometrical body, which can be patternedto different shapes, and is composed of one material or a combination ofmaterials. The material(s) may be organic or inorganic, molecular orpolymeric. Such an electrochromic element, whether it is composed of onematerial or is an ensemble of more than one material, combines thefollowing properties: at least one material is electrically conductingin at least one oxidation state, and at least one material iselectrochromic, i e, exhibits colour change as a result ofelectrochemical redox reactions within the material.

Electrochemically active element: an “electrochemically active element”according to the present invention, is an element having parameterswhich can be switched or altered by means of redox reactions in theelement. In order to facilitate said reactions, the active elements aregenerally in contact with an electrolyte. The elements can for examplebe covered by a solidified electrolyte, as defined below. Typically, theswitchable parameters include electrical conductivity and/or opticalappearance, i.e. colour or brightness. The above defined “electrochromicelement” is one example of an electrochemically active element, whereinthe optical appearance is the exploited parameter. As such, theelectrochromic element may, of course, be utilised in any type ofelectrochromic pixels, e.g. lateral pixels in which the electrodes arearranged side by side in a common plane and vertical pixels in which theelectrodes are sandwiched on top of each other. Another example ofelectrochemically active elements is found in electrochemicaltransistors or diodes, wherein the exploited parameter is the electricalconductivity and the electrochemically active element is used to providea transistor channel. As is readily appreciated by the skilled man,electrochemically active elements are to be found in many differentapplications, and the common denominator is that they have propertieswhich are switchable by means of redox reactions. Solidifiedelectrolyte: for the purposes of the invention, “solidified electrolyte”means an electrolyte, which at the temperatures at which it is used issufficiently rigid that particles/flakes in the bulk therein aresubstantially immobilised by the high viscosity/rigidity of theelectrolyte and that it doesn't flow or leak. In the preferred case,such an electrolyte has the proper Theological properties to allow forthe ready application of this material on a support in an integral sheetor in a pattern, for example by conventional printing methods. Afterdeposition, the electrolyte formulation should solidify upon evaporationof solvent or because of a chemical cross-linking reaction, broughtabout by additional chemical reagents or by physical effect, such asirradiation by ultraviolet, infrared or microwave radiation, cooling orany other such. The solidified electrolyte preferably comprises anaqueous or organic solvent-containing gel, such as gelatine or apolymeric gel. However, solid polymeric electrolytes are alsocontemplated and fall within the scope of the present invention.Furthermore, the definition also encompasses liquid electrolytesolutions soaked into, or in any other way hosted by, an appropriatematrix material, such as a paper, a fabric or a porous polymer. In someembodiments of the invention, this material is in fact the support uponwhich the electrochemical pixel device is arranged, so that the supportforms an integral part of the operation of the device.

Electrodes: “electrodes” in devices according to the invention arestructures that are composed of an electrically conducting material.Such electrodes allow the application of an external voltage toelectrolyte, whereby an electric field within the solidified electrolyteis sustained for a time period long enough for the desiredelectrochemical reactions to occur. In some applications, electrodesmight form part of, or even constitute, electrochemically activeelements and/or electrochromic elements.

Direct electrical contact: Direct physical contact (common interface)between two phases (for example electrode and electrolyte) that allowsfor the exchange of charges through the interface. Charge exchangethrough the interface can comprise transfer of electrons betweenelectrically conducting phases, transfer of ions between ionicallyconducting phases, or conversion between electronic current and ioniccurrent by means of electrochemistry at an interface between for exampleelectrode and electrolyte, electrolyte and electrochromic element, orelectrolyte and electrochemically active element, or by occurrence ofcapacitive currents due to the charging of the Helmholtz layer at suchan interface. Colour change: when reference is made to “colour change”,this is also meant to include changes in optical density or reflectance,so that “colour change” for example takes into account changes from blueto red, blue to colourless, dark green to light green, grey to white ordark grey to light grey alike.

Adhesion promoter: An adhesion promoter is a material capable ofincreasing the adhesion between the PEDO-PSS layer and an additionallayer of another material. Without wishing to be bound by this theory,it is thought that this effect is achieved through:

1. Changing the surface energies. For example, rendering the hydrophilicPSS-rich PEDOT-PSS surface more hydrophobic; and/or

2. The creation of an interfacing layer between the PEDOT-PSS layer andthe additional layer, which interface layer comprises a mixture ofPEDOT-PSS and the other material. For example, a material (such aspolystyrene) slightly soluble in the solvent(s) (e.g. toluene) used todeposit the additional layer (PANI).

Depending on the degree of hydrophobicity wanted/needed and depending onwhat materials to deposit on top of the PEDOT-PSS different amounts ofthese materials or mixtures of these materials can be added. Examples ofmaterials to be used as adhesion promoters include polystyrene,different latex formulations, PMMA (poly(methylemetaacrylate)),polyurethanes, polyglycol esters, N-vinyl lactams, gelatine, a gelatinederivative, polyacrylic acids or esters, polymethacrylic acid,poly-(vinylpyrrolidone), polysaccharides, hydroxyethylcellulose andother cellulos derivatives, polyacrylamides, polyurethanes,polypropylene oxides, polyethylene oxides, poly(styrene sulphonic acid),poly-(styrene sulphonic esters), poly(vinyl alcohol esters) andpoly(vinyl alcohol) and derivatives, salts, blends and copolymersthereof; and may optionally be cross-linked. The functioning of generaladhesion promoters is described in litterature, for example in “Adhesionand Adhesives Technology: An Introduction, 2nd Ed”, by Alphonsus V.Pocius, ISBN: 1-569-90319-0.

Materials

Preferably, the solidified electrolyte in electrochromic devicecomprises a binder. It is preferred that this binder have gellingproperties. The binder is preferably selected from the group consistingof gelatine, a gelatine derivative, polyacrylic acid, polymethacrylicacid, poly(vinylpyrrolidone), polysaccharides, polyacryl-amides,polyurethanes, polypropylene oxides, polyethylene oxides, poly(styrenesulphonic acid) and poly(vinyl alcohol) and salts and copolymersthereof; and may optionally be cross-linked. The solidified electrolytepreferably further comprises an ionic salt, preferably magnesiumsulphate if the binder employed is gelatine. The solidified electrolytepreferably further contains a hygroscopic salt such as magnesiumchloride to maintain the water content therein.

In preferred embodiments, the electrochromic element for use in theelectrochromic device of the present invention comprises, aselectrochromic material, an electrochromic polymer which is electricallyconducting in at least one oxidation state, and optionally alsocomprises a polyanion compound. Electrochromic polymers for use in theelectrochromic element of the invention are preferably selected from thegroup consisting of electrochromic polythiophenes, electrochromicpolypyrroles, electrochromic polyanilines, electrochromicpolyisothianaphthalenes, electrochromic polyphenylene vinylenes andcopolymers thereof, such as described by J C Gustafsson et al in SolidState Ionics, 69, 145-152 (1994); Handbook of Oligo- and Polythiophenes,Ch 10.8, Ed D Fichou, Wiley-VCH, Weinhem (1999); by P Schottland et alin Macromolecules, 33, 7051-7061 (2000); Technology Map ConductivePolymers, SRI Consulting (1999); by M Onoda in Journal of theElectrochemical Society, 141, 338-341 (1994); by M Chandrasekar inConducting Polymers, Fundamentals and Applications, a PracticalApproach, Kluwer Academic Publishers, Boston (1999); and by A J Epsteinet al in Macromol Chem, Macromol Symp, 51, 217-234 (1991). In apreferred embodiment, the electrochromic polymer is a polymer orcopolymer of a 3,4-dialkoxythio-phene, in which said two alkoxy groupsmay be the same or different or together represent an optionallysubstituted oxy-alkylene-oxy bridge. In some embodiments, theelectrochromic polymer is a polymer or copolymer of a3,4-dialkoxythiophene selected from the group consisting ofpoly(3,4-methylenedioxythiophene), poly(3,4-methylene-dioxythiophene)derivatives, poly(3,4-ethylenedioxythio-phene),poly(3,4-ethylenedioxythiophene) derivatives,poly(3,4-propylenedioxythiophene), poly(3,4-propylenedi-oxythiophene)derivatives, poly(3,4-butylenedioxythio-phene),poly(3,4-butylenedioxythiophene) derivatives, and copolymers therewith.The polyanion compound is then preferably poly(styrene sulfonate). As isreadily appreciated by the skilled man, in alternative embodiments ofthe invention, the electrochromic material comprises any non-polymermaterial, combination of different non-polymer materials, or combinationof polymer materials with non-polymer materials, which exhibitconductivity in at least one oxidation state as well as electrochromicbehaviour. Electrochromic elements comprising combinations of more thanone polymer material, such as polymer blends, or several layers ofelectrochromic materials, wherein the different layers consist of thesame material or different materials, e g one layer each of twodifferent electrochromic polymers, are also contemplated.

For example, one could use a composite of an electrically conductingmaterial and an electrochromic material, such as electrically conductiveparticles such as tin oxide, ITO or ATO particles with polymer ornon-polymer electrochromic materials such as polyaniline, polypyrrole,polythiophene, nickel oxide, polyvinylferrocene, polyviologen, tungstenoxide, iridium oxide, molybdenum oxide and Prussian blue (ferricferrocyanide). As non-limiting examples of electrochromic elements foruse in the device of the invention, mention can be made of: a piece ofPEDOT-PSS, being both conducting and electrochromic; a piece ofPEDOT-PSS with Fe²⁺/SCN⁻, PEDOT-PSS being conducting and electrochromicand Fe²⁺/SCN⁻ being an additional electrochromic component (see below);a piece composed of a continuous network of conducting ITO particles inan insulating polymeric matrix, in direct electrical contact with anelectrochromic WO₃-coating; a piece composed of a continuous network ofconducting ITO particles in an insulating polymeric matrix, in contactwith an electrochromic component dissolved in an electrolyte.

Some embodiments of the invention comprise a further electrochromicmaterial for realisation of pixel devices with more than one colour.This further electrochromic material can be provided within theelectrochromic element or the solidified electrolyte of theelectrochromic device, which then for example comprises anelectrochromic redox system, such as the redox pair of colourless Fe²⁺and SCN⁻ ions on one hand, and of red Fe³⁺(SCN)(H₂O)₅ complex on theother. By way of further, non-limiting example, such materials may beselected from different phenazines such asDMPA-5,10-dihydro-5,10-dimethylphenazine,DEPA-5,10-dihydro-5,10-diethyl-phenazine andDOPA-5,10-dihydro-5,10-dioctylphenazine, fromTMPD-N,N,N′,N′-tetramethylphenylenediamine,TMBZ-N,N,N′,N′-tetramethylbenzidine, TTF-tetrathiafulvalene,phenanthroline-iron complexes, erioglaucin A, diphenylamines,p-ethoxychrysoidine, methylene blue, different indigos andphenosafranines, as well as mixtures thereof.

As described above, the electrochromic device of the invention maycomprise a redox active material for reasons other than additionalcolouring effects. This redox active material may be the same ordifferent from any of the further electrochromic materials listedimmediately above. Thus, any suitable anti-oxidant or anti-reductant maybe used, for example organic substances like vitamin C, alcohols,polyalcohols (e g glycerol) or sugars, the alcohols, polyalcohols orsugars where appropriate being present at a high pH, conjugatedpolymers, oligomers and single molecules; inorganic substances likesalts comprising species that may be oxidised (e g Fe²⁺ to Fe³⁺, Sn²⁺ toSn⁴⁺), metal clusters (e g a Cu cluster or a Fe cluster), or saltscomprising species that may be reduced (e g Fe³⁺ to Fe²⁺, Sn⁴⁺ to Sn²⁺);metal organic complexes like ferrocenes, phthalocyanines,metallo-porphyrines.

In electrochemical pixel devices of the invention, it is preferred thatthe electrochromic material in the electrochromic device comprises anelectrochromic polymer. The support in some embodiments of theelectrochemical pixel device of the present invention is preferablyselected from the group consisting of polyethylene terephthalate;polyethylene naphthalene dicarboxylate; polyethylene; polypropylene;paper; coated paper, e g coated with resins, polyethylene, orpolypropylene; paper laminates; paperboard; corrugated board; glass andpolycarbonate. The support is also preferably reflective.

Embodiment of an Electrochemical Pixel Device

A typical electrochemical pixel device according to an embodiment of theinvention is shown schematically in FIG. 1. The electrochemical pixeldevice 1 is constructed through patterning of a suitable material (seeabove), and comprises an electrochemical transistor device (2-5, 10-11)and an electrochromic device (6-9). The electrochemical transistordevice, which does not form part of the present invention, comprises asource contact 2 and a drain contact 3. Between, and in directelectrical contact with, the source and drain contacts is arranged anelectrochemically active element 4, the conductivity of which may bealtered through application of a gate voltage to a positive gateelectrode 5. The electrochemically active element 4 and part of thepositive gate electrode 5 are covered with a layer of solidifiedelectrolyte 10. In this embodiment, the source and drain contacts 2,3and the electrochemically active element 4 are all formed by acontinuous piece of the material. This piece is separated by a narrowgap from the gate electrode 5, so that there is no direct electricalcontact between the electrochemically active element 4 and the gateelectrode 5.

The electrochromic device comprises an electrochromic element 6, as wellas two electrodes 7,8. Covering the electrochromic element 6 and thefirst electrode 7 is a layer of solidified electrolyte 9. There is nodirect electrical contact between the first electrode 7 and theelectrochromic element 6, but between the electrochromic element 6 andthe second electrode 8. The first electrode 7 of the electrochromicdevice is in direct electrical contact with, or rather coincides with,the source contact 2 of the electrochemical transistor device.

Upon function of the electrochemical pixel device 1, a colouring ordecolouring current is supplied to the electrochromic element 6 throughapplication of a voltage between drain contact 3 and electrode 8,corresponding to a drain-source-voltage V_(ds). The current actuallysupplied to the electrochromic element 6 is controlled by theconductivity in the electrochemically active element 4. Thisconductivity, in turn, is controlled by a gate voltage V_(g) at thepositive gate electrode 5. The gate voltage V_(g) may, in certainembodiments, be applied between the positive gate electrode 5 and asecond, negative gate electrode 11, which may or may not be in directelectrical contact with the electrochemically active element 4.Alternatively, the gate voltage is applied between the positive gateelectrode 5 and either of the source contact 2 or the drain contact 3.

The above described embodiment of the electrochromic device is thusinterconnected with a transistor, which is used for driving the device.The transistor does however not form part of the present invention, butonly serves as an example of a possible application for the invention.Of course, in many applications the transistor can be left out. This isthe case, for example, when the electrochromic device is to be passivelyaddressed. Such a passive device of course can be formed similar to theabove embodiment, only by omitting the transistor. An embodiment of suchan electrochromical device is illustrated in FIG. 2, which in effect isan identical device as the one shown in FIG. 1, but having thetransistor omitted.

In an experiment using the above embodiment of an electrochemical pixeldevice according to the invention, the device was manufactured asfollows: a starting material of Orgacon™ EL-350 foil, commerciallyavailable from Agfa and comprising the conducting and electrochromicpolymer PEDOT-PSS (poly-(3,4-ethylendioxy-thiophene) doped withpoly(styrene sulfonate)) was used. Patterning of the PEDOT-PSS substratewas done using a plotter tool equipped with a scalpel. The electrolyteused was commercially available Blagel™ from Apoteksbolaget, Sweden. Thegel was applied using silk-screen printing with a 45 μm thick, patternedvinyl foil as template. Alternatively, 10% hydroxy ethyl cellulose inwater may be used as the electrolyte gel.

PEDOT-PSS is a material that exhibits a very light, pale blue colour andgood conductivity in its native, partly oxidised state. When thePEDOT-PSS is reduced, its conductivity diminishes greatly, and thematerial is coloured deeply blue. In such PEDOT-PSS pixel devices as theone described with reference to FIG. 1, the electrochromic device istypically driven with V_(ds) voltages between 1.5 and 2 V, and thedisplay area varies between 1 and 2 cm². The electrochromic element 6 inthis case is reduced and switched to a deep blue colour. An electrode 7converts the electronic current to ionic current or vice versa is alsopresent. In experiments with the PEDOT-PSS pixel, the current passingthrough the electrochromic device was about 200-300 μA in the beginning,at a V_(ds) of 2 V and an electrochromic element area of 1-2 cm². Afterapproximately 10 s it was fully switched and saturated. The currentflowing through the electrochromic device in this saturated state wasaround 50 μA. The reason for this current even in the reduced,non-conducting state of PEDOT-PSS is leakage from the display cell.

In experiments switching the transistor, the electrochemical transistordevice was driven by gate voltages between 0 and 1.5 V. At a gatevoltage of 0 V, the electrochemically active element was fullyconducting, and at 1.5 V, it was in its “off” state. Already at 0.3-0.4V it was evident from the appearance of blue colouring that thetransistor channel was being reduced, which corresponds to an increasedresistance. The resistance in the transistor channel was approximatelyaround 10 kΩ in its conducting state, which corresponded to a current of200 μA at 2 V. In the cut-off state, at gate voltages of around 1.5 V,the resistance was greatly increased. Current values of around 200 nAwere reached, corresponding to a resistance of 10 MΩ. The on/off-ratiofor the electrochemical transistor device part of the electrochemicalpixel device was thus 1000 in this case. Furthermore, extremeon/off-ratios of 105 in the electrochemical transistor were reached withcomponents made in alternative ways.

Some working characteristics of this electrochemical pixel device:

-   -   The transistor channel was conducting at a gate voltage, V_(g),        of 0 V, and substantially non-conducting at a V_(g) of 1 V.    -   If already reduced, i e deep blue, the electrochromic element        decoloured at a V_(ds) of 0 V, otherwise nothing happened. At a        V_(ds) of 2 V, electrochemistry occurred, and the electrochromic        element changed to its reduced, deep blue state, and remained in        this state as long as the voltage was applied.

Effects of four possible combinations of voltages applied to the pixel:

V_(g)=0 V, V_(ds)=0 V; nothing happens, or the pixel decolours if it wasreduced from the beginning.

V_(g)=0 V, V_(ds)=2 V; colours the pixel, which then remains in thisstate.

V_(g)=1 V, V_(ds)=0 V; the transistor channel is renderednon-conducting. If the pixel is already reduced, the increased impedancein the channel keeps the charges inside the pixel area.

V_(g)=1 V, V_(ds)=2 V; nothing happens.

FIG. 3 illustrates a electrochemical device, in which theelectrochemical element 6 and the electrodes 7 and 8 are all placed sideby side, and the electrochromical element is place at a distance fromelectrode 7 and in direct electrical contact with electrode 8.

FIG. 4 illustrates an alternative arrangement, in which theelectrochemically active element 6 is instead placed on top of theelectrode 8. FIG. 5 illustrates a similar arrangement as the oneillustrated in FIG. 4, but having an additional, protective layer 12deposited on electrode 7. The protective layer 12 serves to protect theelectrode 7 from being overoxidised when exposed to an oxidativecurrent.

FIG. 6 illustrates an inventive electrochemical element, comprisingmixture layer 602 of PEDOT-PSS mixed with polystyrene and a protectivelayer 601 comprising PANI. At the interface between layers 601 and 602there is formed an intermediate layer 603, which is the result ofsolvents in the PANI soloutin dissolving and mixing with the surface ofthe PEDOT-PSS layer. The creation of such an intermediate layer isactually the reason explaining the improved adhesion of the PANI layerto the PEDOT-PSS layer. However, for other material combinations such aintermediate layer 603 might not be formed, the layers 601 and 602instead being in direct contact with each other. The protective PANIlayer serves to protect the mixture layer from being overoxidised, andalso provides the element with switchable redox properties.

In the following three examples, reference will be made to a testarchitecture which is shown in FIG. 7. The test architecture thuscomprises a counter electrode 702 and a pixel electrode 701. On thepixel electrode, an electrochromic element 703 is defined, and on thecounter electrode a counter electrode area 704 is defined. This counterelectrode area 704 is actually also an electrochromic element in thefollowing examples. On top of the electrochromic element and the counterelectrode area a solidified electrolyte 705 is deposited. In all threeexamples, the electrolyte is based on water and contains 10% by weightof hydroxyethyl cellulose, 20% by weight of glycerol, 8% by weight ofsodium citrate salt (Na-citrate). The pH value of the electrolyte isadjusted to between 4 and 5 by adding H₃PO₄ prior to applying theelectrolyte onto the device.

Improved Lateral Electrochemical Display Cell

Thus, referring to FIG. 7, an electrochromic device having a lateraldesign is shown. The electrodes 701 and 702 were formed from an Orgacon™EL-350 foil. In this case the PEDOT-PSS functions both as conductors andelectrodes in the device. The counter electrode 702 was coated withPANIPOL T™ deposited by drop casting. An identical device is made up asreference from the same components but without the PANI layer.

The pixels were switched continuously in forward bias 1.5V where theelectrochromical element turns transparent and in backward bias 9.0Vwhere the pixel element turns blue. The cycling was continued for 1 000cycles and the pixel and counter electrodes were checked foroveroxidation. The PANI covered counter electrode was nearly unaffected(less than 1% degradation of the active area) but the counter electrodeof the reference device was completely degraded after 1000 switches. ThePANI coated device actually continued to switch for over 10 000 switchesand its lifetime was limited not due to overoxidation but due todelamination of the PANI from the PEDOT-PSS layer. This delamination isbelieved to be the effect of, at least partially, the different swellingproperties of the two materials, PEDOT-PSS and PANI, which causedmechanical strains during electrochemical switching.

Improved Adhesion in a Lateral Electrochemical Display Cell

The same device architecture as in the example above is utilized, withthe exception that the PEDOT-PSS used in the counter electrode part ofthe device here was a screen printable paste, Orgacon EL™, as suppliedby Agfa. On top of the screen-printed counter electrode part of thedevice was drop casted a PANIPOL T™ solution. An identical device, areference, was made up from the same components but the screen-printedPEDOT-PSS layer was replaced by Orgacon EL350™. Tape tests performed byripping of tapes adhered to the elements showed much improved adhesionof the PANI onto the screen-printed paste as compared to the Orgacon™EL-350 foil.

The pixel was switched continuously in forward bias 1.5V where the pixelelements turn transparent and in backward bias 9.0V were the pixelelements turn blue. The cycling was continued for 10 000 cycles and thepixel and counter electrode were checked for overoxidation anddelamination. No significant delamination or degradation of the counterelectrode could be observed. The device was kept switching for over 25000 switches and still no significant degradation of the counterelectrode or delamination could be observed.

Improved Contrast Ratio in a Lateral Electrochemical Display Cell

The same architecture as in the above example was used. The electrodeswere formed from Orgacon™ EL-350. On the counter electrode area and onthe electrochromic element an additional PANIPOL T™ layer was depositedby drop casting. An idenitacal device, a reference, was made up from thesame components but the PANI layer on the pixel element was omitted. Thepixels were switched continuously in forward bias 1.5V where the pixelelement turns transparent and in backward bias 1.5V were the pixelelement turns blue. The cycling was continued for 10 cycles when thepixel and counter electrodes were assumed to have reached “equilibriumconditions”. The contrast was measured using a spectrometer. Thewavelength used was 640 nm. The contrast ratios were compared, in aforward bias of 1.5 V were the PEDOT-PSS pixel turns transparent and thePANI coated PEDOT-PSS pixel becomes blue and in a backward bias of 1.5 Vwere the PEDOT-PSS pixel turns blue and the PANI coated PEDOT-PSS pixelbecomes transparent. The different contrasts using the Lab vector lengthin the CIE-Lab colour coordinates were for the PEDOT-PSS pixel 4 and forthe PANI coated PEDOT-PSS pixel it was 20.

1. An electrochromic device comprising: at least one electrochromicelement comprising (i) at least one material that is electricallyconducting in at least one oxidation state and (ii) at least oneelectrochromic material, wherein said materials (i) and (ii) can be thesame or different; at least one layer of a solidified electrolyte whichis in direct electrical contact with said electrochromic element; and atleast two electrodes comprising PEDOT-PSS, arranged side by side in acommon plane and adapted for application of a voltage therebetween, oneof said electrodes being in direct electrical contact with a componentselected from said electrochromic element(s) and the other electrode(s)being in direct electrical contact with a component selected from saidelectrolyte layer(s) and said electrochromic element(s).
 2. Anelectrochromic device according to claim 1, in which the electrodes andthe electrochromic element(s) are arranged side by side in a commonplane.
 3. An electrochromic device according to claim 1, in which theelectrochromic material is an electrochromic polymer.
 4. Anelectrochromic device according to claim 1, in which the electrochromicelement comprises a polyanion compound.
 5. An electrochromic deviceaccording claim 4, in which said polyanion compound is a poly(styrenesulfonate) or a salt thereof.
 6. An electrochromic device according toclaim 1, in which the electrochromic element is formed from the samematerial as the electrodes.
 7. An electrochromic device according toclaim 1, in which the electrochromic element comprises polyaniline. 8.An electrochromic element according to claim 1, in which the electrodesare formed out PEDOT-PSS.
 9. An electrochromic element according toclaim 1, in which the electrodes are formed out of a mixture comprisingPEDOT-PSS and polystyrene.
 10. An electrochromic element according toclaim 7, in which said polyaniline is cast from a toluene solution. 11.An electrochemical pixel device according to claim 1, in which thesolidified electrolyte in the electrochromic device comprises a binder.12. An electrochemical pixel device according to claim 11, in which saidbinder is a gelling agent selected from the group consisting ofgelatine, a gelatine derivative, polyacrylic acid, polymethacrylic acid,poly(vinylpyrrolidone), polysaccharides, polyacrylamides, polyurethanes,polypropylene oxides, polyethylene oxides, poly(styrene sulphonic acid)and poly(vinyl alcohol), and salts and copolymers thereof.
 13. Anelectrochemical pixel device according claim 1, in which the solidifiedelectrolyte in the electrochromic device comprises an ionic salt.
 14. Anelectrochemical pixel device according claim 1, arranged on a support.15. An electrochemical pixel device according to claim 14, in which saidsupport is selected from the group consisting of polyethyleneterephthalate, polyethylene naphthalene dicarboxylate, polyethylene,polypropylene, polycarbonate, paper, coated paper, resin-coated paper,paper laminates, paperboard, corrugated board and glass.
 16. Anelectrochemical pixel device according to claim 14 in which said supportis reflective.
 17. An electrochemically active element comprising: afirst layer comprising PEDOT-PSS mixed with an adhesion promoter; and asecond layer comprising PANI, the second layer being deposited on top ofand in direct electrical contact with the first layer.
 18. Anelectrochemically active element according to claim 17, wherein theadhesion promoter comprises polystyrene.
 19. An electrochemically activeelement according to claim 17, wherein said PANI is cast from a toluenesolution.
 20. An electrochemically active element according to claim 17,which forms part of a pixel device.
 21. An electrochemically activeelement according to claim 20, said pixel device being a lateral pixeldevice.
 22. An electrochemically active element according to claim 17,said pixel device being a vertical pixel device.
 23. Anelectrochemically active element according to claim 17, which forms partof a transistor device.
 24. An electrochemically active elementaccording to claim 17, which forms part of a diode device.
 25. Anelectrochromic device according to claim 2, in which the electrochromicmaterial is an electrochromic polymer.
 26. An electrochromic deviceaccording to claim 2, in which the electrochromic element comprises apolyanion compound.
 27. An electrochromic device according to claim 3,in which the electrochromic element comprises a polyanion compound. 28.An electrochemical pixel device according to claim 15, in which saidsupport is reflective.
 29. An electrochemically active element accordingto claim 18, wherein said PANI is cast from a toluene solution.
 30. Anelectrochemically active element according to claim 18, which forms partof a pixel device.
 31. An electrochemically active element according toclaim 19, which forms part of a pixel device.